1. Field of the Invention
The present invention relates to methods and apparatus for controlling the flow and the monitoring the pressure of an infusion solution during cardioplegia procedures. More particularly, the present invention relates to a stopcock for effecting such functions where retrograde and antegrade cardioplegia procedures are being performed sequentially in the same surgery.
2. Background Art
It is recognized in cardiac surgery that the myocardial necrosis that occurs during surgery is due to the isolation of the heart from its life-giving blood supply. To reduce this damage to heart tissue it is known to infuse a cardioplegic solution into the blood vessels through which nutrients would normally reach the tissue of the heart. Cardioplegic solutions typically are cooled fluids containing potassium, magnesium procaine, or a hypocalcemic composition. The solutions still the heart and suppress tissue metabolism thermally and chemically.
Cardioplegia may be administered in an antegrade manner through coronary arteries in the normal direction of blood flow, or in a retrograde manner through coronary veins in a direction opposite to normal blood flow. In both procedures, before cardioplegia equipment is located in the heart, the heart is cannulated to create a cardiopulmonary bypass about the heart through a life-support system. That system typically includes an oxygenator, a pump, a blood filter, and a cardiotomy reservoir. Cannulation is effected using one or more venous return catheters and an aortic arch cannula. Suitable clamping is effected of the blood vessels involved so as to isolate the heart from blood flow.
In antegrade cardioplegia, a single cannula is inserted into the aortic root, and the cardioplegic solution is infused therethrough into the coronary arteries in the normal direction of blood flow. An antegrade cardioplegia cannula suitable for this purpose is disclosed in a copending U.S. Pat. application filed concurrently herewith and entitled "Antegrade Cardioplegia Cannula" which is incorporated herein by reference.
To enable a flow through of the cardioplegic solution, antegrade cardioplegia procedures are vented on the right side of the heart. This can be accomplished utilizing either a separate right ventricle vent, or a vent built into one of the other catheters located there. These might include the one or more of the venous return catheters utilized to bypass the heart to the life support system, or, if both types of cardioplegia procedure are being used in the same operation, the catheter used for retrograde cardioplegia. As the left side of the heart is normally exposed to relatively high fluid pressures, it has not routinely been the case that the pressure of cardioplegia solution in the heart in an antegrade cardioplegia procedure is consistently monitored.
In retrograde cardioplegia a balloon catheter is inserted through the right atrium into the coronary sinus. Inflation of the balloon stops the fluid flow from the tip of the catheter into the right atrium. The cardioplegic solution is administered through the catheter into the heart through the coronary veins branching from the coronary sinus in a direction reversed to that of normal blood flow. A suitable retrograde cardioplegia catheter for this purpose is disclosed in copending U.S. Pat. application Ser. No. 187,230, filed Apr. 28, 1988 and entitled "Retrograde Venous Cardioplegia Catheters and Methods For Use And Manufacture".
To enable a flow through of cardioplegic solution, in retrograde cardioplegia procedures the left side of the heart is vented, either using a separate left ventricular vent or by way of a vent built into other catheters or cannulas being used on that side of the heart. These might include the aortic arch cannula or, if both retrograde and antegrade cardioplegia are being employed in the same operation, the antegrade cardioplegia cannula. As the venous structures on the left side of the heart are not routinely subjected to high-fluid pressures, the monitoring of the cardioplegic solution in the heart at this point is essential and always undertaken.
While retrograde and antegrade cardioplegia each have particular strengths and weaknesses, if coronary artery blockage is major, the use of both procedures individually in sequence is necessitated, if heart tissues on the downstream sides of the arterial blockages is to be perfused by the cardioplegic solution and thus fully protected from myocardial necrosis.
Typically, when both procedures are to be employed, a single source of cardioplegic solution is Y-connected to the retrograde catheter and to the antegrade cannula. A clamp in each leg of the Y-connection permits the solution source to be connected to each selectively. To simplify matters, a single pressure monitor is employed and the fluid pressure on the left, arterial, or antegrade side is quite often simply not monitored at all. If fluid pressure on both sides is to be monitored, two monitors are used or a Y-connection similar to that used with a single source of cardioplegic solution is employed.
Where antegrade and retrograde cardioplegia procedures are utilized in sequence, the change from one to the other can be a cumbersome, time-consuming, and risk-filled undertaking. It is necessary upon switching from one procedure to the other to cut off fluid communication in the infusion tubing and in infused and then to open the corresponding tubing to the other side of the heart.
While the time in which to do so is of some concern, the major problem with this process is the break it causes in the concentration of the surgeon. In addition, the switchover is dangerous. For example, the failure to close one infusion tubing before opening the other could lead to infusion occurring at both sides of the heart, which can literally blow up the delicate blood supply tissues thereof. Another risk is that the pressure monitor will somehow become coupled to the side of the heart not being infused. Particularly where infusion is occurring on the right, venous, or retrograde side, this is a danger, as the failure to detect high pressures on the right side of the heart can result in edema or in tissue tearing in the venous structure of the heart.
These complications have led many surgeons to forego the use or the option to use both retrograde and antegrade cardioplegia in a single surgery. Thus, the maximum known protection from myocardial necrosis is not utilized and the methods and apparatus available in the art of cardiac surgery must regretfully be assessed as not keeping current.